1. Field of the Invention
The present invention relates to a surface texture measuring instrument. Specifically, the present invention relates to a surface texture measuring instrument including an exchangeable measurement arm having a stylus to be brought into contact with a surface of an object to be measured.
2. Description of Related Art
There has been known a surface texture measuring instrument that measures a surface texture such as a surface profile and surface roughness of an object by moving a stylus along a surface of an object to be measured while being in contact with the surface, detecting the displacement of the stylus (in a direction perpendicular to a moving direction of the stylus) caused by the surface profile or surface roughness of the object, and measuring the surface texture based on the displacement of the stylus.
Some of the surface texture measuring instrument include styluses (measurement arms) having various profiles prepared in advance and exchanged depending on profiles of measurement portions, so that measurement portions of an object having various profiles can be measured by the most suitable stylus for the profiles of the measurement portions.
For instance, Patent Literature 1 (DE19617022C1) has proposed a contour measuring instrument including: a column standing upright on a base; a holder provided on the column to be vertically movable via an adjustment instrument; a housing provided to the holder; a see-saw provided in the housing to be horizontally movable via a linear motor; a measurement arm connected to the see-saw via a connecting unit outside the housing; and a stylus provided at an end of the measurement arm, in which the measurement arm is exchangeable outside the housing.
In the aforementioned contour measuring instrument, the measurement arm is exchangeable outside the housing. Accordingly, although exchange of the measurement arm is easy, an error is likely to be caused because a detector detecting displacement of the measurement arm including the stylus to be brought into contact with an object is offset from an axis of the measurement arm and the stylus.
Moreover, since the connecting unit provided with a detachable measurement arm is disposed outside the housing, when external force acts on the measurement arm and the stylus to detach the measurement arm from the connecting unit, the measurement arm is likely to fall. In such a case, the measurement arm and the stylus may be damaged. Furthermore, since the connecting unit is exposed outside the housing, the connecting unit may interfere with the object in measurement to be damaged and easily becomes dirty depending on external environment in which the connecting unit is used.
Moreover, in the surface texture measuring instrument such as the aforementioned contour measuring instrument, it is required to adjust pressure (i.e., measurement force), by which the stylus is brought into contact with the surface of the object, to the most suitable measurement force for a material and a profile of the object.
In general, when the measurement arm is exchanged, a weight of an exchanged measurement arm is often different from a weight of the original measurement arm, whereby the exchanged measurement arm becomes off balance to cause an error in measurement. For this reason, at each time of the exchange of the measurement arm, balance of the measurement arm needs to be adjusted to keep the measurement arm substantially horizontal, before the measurement force is adjusted.
Typically, a measuring force adjusting mechanism needs to be adjusted after the exchange of the measurement arm. Specifically, the stylus at the end of the measurement arm is put on a measuring instrument for measuring force (e.g., an electronic scale), and while keeping this condition, the measuring force adjusting mechanism is adjusted such that a value displayed on the measuring instrument is 0. Accordingly, the aforementioned surface texture measuring instrument shows a poor usability and a poor operational efficiency.